This invention relates generally to controlling the movement of a vehicle along a guideway, and more specifically to methods and systems for utilizing variable rate communication timeouts in vehicle control systems.
At least some known rail traffic signal systems use an extensive array of wayside equipment to control railway traffic and maintain safe train separation. In these known systems, railway control is achieved by detecting the presence of a train, determining a route availability for each train, conveying the route availability to a train's crew, and controlling the movement of the train in accordance with the route availability.
The presence of a train is typically detected directly through a sensor device, or track circuit, associated with a specific section of the rails, referred to as a block. For example, the presence of a train may cause a short in a block's track circuit. In this manner, the occupancy of each block is determined. Vital decision logic is employed, utilizing the block occupancy information in conjunction with other information provided, such as but not limited to track switch positions, to determine a clear route availability for trains. The route availability information is then conveyed to a train crew through a communication-based train control (CBTC) system using a wireless transmission circuit, such as a radio or cellular telephone. The CBTC system generally includes a computer at one or more fixed locations determining the movement authority and/or constraints applicable to each specific train. The computer then transmits this train-specific information in unique messages addressed or directed to each individual train. In some known systems such as an incremental train control system (ITCS), an authority message is broadcast to any train that may be within receiving distance. The train movement is then controlled by crew actions based on displayed aspect information and, in case of failure by the crew to take necessary actions, through optional speed enforcement.
In the current ITCS approach, all authority and occupancy reporting vital train to wayside and wayside to train communications have a preset timeout value. If data is not received within this time, safety critical actions are taken, generally in the form of a penalty brake. However, in portions of the track system, the timeout value is overly strict and has a negative impact on system performance.